1. Field of the Invention
THE PRESENT INVENTION relates to a safety arrangement, and more particularly relates to a safety arrangement incorporated in a vehicle seat.
2. Description of Related Art
It is known to use, in a vehicle, a seat which is provided with a head-rest mounted on the back of the seat, the head-rests being adapted to move forwardly in the event that a rear impact should occur to provide protection for the occupant of the seat in order to minimise, or obviate whiplash injuries. Such a head-rest may be termed an “active” head-rest.
It has been proposed previously to provide an active head-rest which is activated when the occupant of the seat is pressed into the back-rest of the seat, as a consequence of a rear impact situation. Such a prior proposed arrangement incorporates a head-rest which is mounted for pivotal movement about a horizontal axis adjacent the top of the seat, the head-rest being connected, by appropriate arms, to a pressure plate which is mounted within the back-rest of the seat. As the torso of the occupant of the seat is pressed into the back-rest of the seat during a rear impact, the pressure plate is moved in a rearward direction, thus causing the head-rest itself to move forwardly, so that the head-rest is brought into a position immediately behind the head of the occupant. An arrangement of this type is shown in U.S. Pat. No. 5,378,043.
This prior proposed arrangement is intended for use in the front seat of a motor vehicle. Typically the front seat of a motor vehicle has a back-rest formed from an inverted “U”-shaped frame, with appropriate springing and padding filling the area between the parallel arms of the frame. Typically both the forward facing side and the rearward facing side of the back-rest are made to be soft and flexible so that the seat is not only comfortable for a person sitting in the seat, but also is not uncomfortable for the knees of a person sitting in the seat behind. Thus, in the prior art arrangement, the pressure plate can move rearwardly relative to the inverted “U”-shaped frame when a rear impact occurs.
In many vehicles, the rear part of the back-rest of a rear seat is constituted by a rigid panel. One reason for this is that typically the rear part of the back-rest of the rear seat forms an upright wall defining part of the boot or trunk. This wall must be sufficiently strong to prevent any luggage present in the boot or trunk from entering the passenger compartment in a frontal impact situation. Also, in many cases the back-rest of the rear seat may fold downwardly, and then the panel at the back of the back-rest forms part of a load-bearing platform.
If a head-rest of the type described in U.S. Pat. No. 5,378,043 were to be mounted in the back-rest of a rear seat, having a rigid rear panel, the pressure plate would, in a rear impact situation, almost immediately engage the rigid rear panel, and thus the head-rest would not be moved sufficiently forwardly to prevent whiplash injuries.
Whilst it might be possible to make the back-rest “thicker”, thus creating more space for movement of the pressure plate, car manufacturers tend to prefer seats that are as thin and as light as possible. Whilst one might contemplate providing a hatch in the rigid plate, adapted to open in the event of a rear impact, to allow the pressure plate to move rearwardly, it is very difficult to provide a hatch whilst still maintaining a rear panel for the seat, which is flat. A flat surface for the rear panel is important when the back-rest of the rear seat is folded forwardly so that the panel forms a load-bearing platform. Also, of course, if the boot or trunk of the vehicle is full of luggage, luggage would be adjacent the hatch and would prevent the hatch from opening. It is to be understood that if the pressure plate is located closer to the front surface of the back-rest of the seat, the pressure plate would prove to be uncomfortable.